Well, they're certainly matured products in that you don't lose things.
Of course you don't find highest performance CPUs and GPUs from them, because they're meant to be lighter devices.
But if your use is lighter like web surfing, video watching, etc or some occasional photo editing, they're basically comparable to normal ultrabooks of same size/weight class.
While giving new usage options.
Though no doubt cheapest ones might have some new problems compared to standard clamshell laptop.
Lenovo X1 Yoga isn't good for giving info about those.